Although the region of contact between two immiscible phases may be very thin, the behavior at this transition area, or interface, is very important. For example, the determination of the interfacial tension of a system can be used as a means of determining necessary types and concentrations of solutions or additives to add to a petroleum-containing reservoir in order to lower the capillary forces preventing oil displacement and to enhance oil recovery from a secondary or tertiary oil recovery process. Common materials used to lower surface or interfacial tension are natural or synthetic surfactants.
The available methods of surface and interfacial tension measurements include the capillary rise, drop-weight and drop-volume, maximum bubble pressure, du Nouy ring, Wilhelmy plate, captive bubble, pendant drop, sessile drop and spinning drop methods. Comparisons of most of these methods are given by J. F. Padday in Surface and Colloid Science, E. Matijevic (Editor), Wiley-Interscience, New York, Vol. 1, p. 101, 1969 and by W. D. Harkins in Physical Methods of Organic Chemistry, A. Weissberger (Editor), Interscience, New York, 1959. These methods of surface tension determination are impractical or inoperative under conditions which approximate or simulate actual petroleum reservoir conditions. It is desired to have an instrument capable of conveniently measuring the following parameters of either interfacial (liquid/liquid) or surface (gas/liquid) tensions, under either dynamic (function of contact time) or static (fixed contact time), and under reservoir conditions of temperature and pressure whether the tension values may be high (80 mN/m), low (1 mN/m) or ultra-low (10.sup.-4 mN/m). An apparatus capable of conveniently measuring the desired interfacial or surface tension values of various materials under reservoir conditions would be very useful in enabling the efficient selection of effective surfactants and other additives for use in a petroleum reservoir to enhance oil recovery therefrom.
In U.S. Pat. No. 4,953,389, to Schurch the substrate surface formed of an agar gel on an inert metal was adequate for maintaining the proper wetting condition under conditions employed therein. This was found not to be the case for measurements at elevated temperatures and furthermore not suitable for some kinds of interfacial tension measurements where chemical materials could diffuse into the gel structure.
Accordingly, it is an object of the present invention to provide a simple apparatus for determining interfacial or surface tensions at the interface between two immiscible fluids. More specifically, it is an object of the present invention to provide a means of determining the interfacial tension between two liquids at realistic petroleum reservoir conditions temperatures and pressures where the interfacial tension may be very low in magnitude.